This grant application proposes the development of two new imaging techniques for bone densitometry and their evaluation by performance comparisons with a commercial bone densitometer. All three techniques will then be used to undertake longitudinal studies of bone remodeling in the rat caused by periods of non-weightbearing and exercise. In addition, the three techniques will undergo a preclinical evaluation using phantoms composed of human anatomical specimens to ascertain the utility of the new techniques for future patient studies. The two new densitometric techniques are based on a dual-energy kinestatic charge detector (KCD) and on a dual-energy charge-coupled device (CCD) camera coupled to an x-ray intensifying screen. The commercial bone densitometer used in the comparison is a LUNAR DPX machine available at the Memphis Metabolic Bone Center. The animal studies will measure the temporal and spatial rates of calcium loss from the trabecular and cortical regions of the femur and tibia during non-weightbearing, and the effects of the type and frequency of exercise in ameliorating adverse bone remodeling. The preclinical studies will involve the use of anatomical phantoms comprising human vertebrae, radii and ulnae that are 1) immersed in various thicknesses of water, and 2) immersed in lesser thicknesses of water and superimposed on anthropomorphic chest and abdominal phantoms. The major impact on health care resulting from this research is expected to arise from the improved accuracy and reduced examination time of the new densitometric modalities, as well as from the new physiological insights gained from bone remodeling research conducted in the animal studies. This proposal is a collaboration of engineers, scientists and physicians from the Departments of Biomedical Engineering, Physiology and Radiology at the University of Tennessee, Memphis.